1. Field of the Invention
The present invention is broadly concerned with position indicating knob assemblies adapted for attachment to rotatable on-off valves in order to indicate via distinct and perceptible indicators the position of the valve in various positions such as valve closed, valve partially opened, and valve full open positions. In preferred forms, the invention is concerned with such knob assemblies, and the combination thereof with valve bodies, wherein the knob assembly includes a differently colored valve position indicator which displays respective colors corresponding to different valve positions.
2. Description of the Prior Art
Emergency oxygen supplies in aircraft are in the form of oxygen cylinders equipped with selectively operable valves. These valves are designed to open gradually in order to protect downstream components from pressure surges. Consequently, the valves typically require multiple rotations of a valve stem to move between closed and open positions. When such cylinders are installed in an aircraft, the valve is supposed to be in the full open position thereof, and it is lock-wired in this position. However, if the valve is only partially opened (e.g., only one revolution in a six revolution to open valve), the pilots panel reading will show the valve opened because positive oxygen pressure would exist, and the valve would be lock wired in this position. However, in the event of an emergency decompression, the partially opened valve would deliver insufficient emergency oxygen, and catastrophic results could ensue.
Conventional knob position indicators use simple on-off position pointers. This method is acceptable for valves that go from full closed to full open in less than one stem revolution. However, valves with greater than one revolution from full closed to full open cannot make use of a simple pointer. In some applications, an electromechanical approach has been utilized to sense the position of the valve via electrical switch components. A disadvantage of this approach is the vulnerability to displacement or misalignment of the switch components, such that the switch contacts close prematurely or not at all. Further, this approach cannot distinguish between three valve conditions (fully closed, partially open and full open) unless multiple switches are used. Finally, the switch concept is dependent on a source of electrical power and also requires circuitry to concert the switch signals to a form perceptible to users.
U.S. Pat. No. 3,910,308 describes a valve signal handle which is capable of indicating fill closed and full open position using different colors. However, this device is incapable of indicating an intermediate valve position between full open and full closed. U.S. Pat. Nos. 3,151,598, 3,183,885, 3,241,515, 3,547,071 and 5,769,118 all describe various valve and turn-indicating units making use of digitized counters. For example, U.S. Pat. No. 3,547,071 describes a turn indicator for showing the number of turns made by a shaft equipped with a knob or the like. A series of indicator numerals are provided so that each time the knob is turned one full revolution a new number is shown. These patents also describe combination devices which not only count revolutions, but also provide angular displacement indicators.